Pll circuit and optical disc apparatus

ABSTRACT

A PLL circuit includes a polyphase reference clock output circuit that outputs reference clocks, a polyphase frequency divider circuit that outputs divided clocks, which is obtained by dividing frequencies of the reference clocks, a selection switch circuit that selects one of the reference clocks or one of the divided clocks, and outputs the selected clock as a selected clock, a digital VCO that uses the selected clock as an operating clock, and outputs delay amount data indicating a phase difference between an output clock and an ideal phase, where the output clock has a frequency that fluctuates according to a value of frequency control input data, and the ideal phase is calculated according to the output clock and the value of the frequency control input data, and a selection circuit that selects and outputs the output clock synchronized with the divided clocks according to the delay amount data.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of co-pending application Ser. No.12/773,971 filed on May 5, 2010 which claims foreign priority toJapanese patent application No. 2009-124160, filed on May 22, 2009. Theentire content of each of these applications is hereby expresslyincorporated by reference.

BACKGROUND

1. Field of the Invention

The present invention relates to a PLL (Phase Locked Loop) circuit andan optical disc apparatus.

2. Description of Related Art

An optical disc apparatus for recording and reproducing data to and froman optical disc media such as CD and DVD is widely used at the moment.Spirals (wobble) of a predetermined cycle are fabricated in groovesformed on the disc surface of an optical disc media. An optical discapparatus provides a wobble signal (hereinafter referred to as arotation synchronizing signal) generated according to this wobble to aPLL circuit, and generates a synchronous clock signal at the time ofrecord and reproduction. The frequency of this rotation synchronizingsignal is different between the outer and the inner circumstance of adisc.

Therefore, the optical disc apparatus includes a PLL circuit whichfluctuates the frequency of a synchronous clock signal according to therotation synchronizing signal. In order to accurately record andreproduce data to and from an optical disc media, such PLL circuit needsto generate a clock signal which synchronizes with a target clock signalwith high phase accuracy.

An example of the PLL circuit which generates a clock signalsynchronized with a reference signal accurately is disclosed in JapaneseUnexamined Patent Application Publication No. 2008-205730. FIG. 17illustrates the configuration of a PLL circuit 1 disclosed in JapaneseUnexamined Patent Application Publication No. 2008-205730. Asillustrated in FIG. 17, the PLL circuit 1 includes a polyphase referenceclock output circuit 10, a digital VCO (Voltage Controlled Oscillator)20, a selection circuit 30, a frequency control terminal 40, and a highprecision clock output terminal 50.

The polyphase reference clock output circuit 10 includes odd number ofinverter circuits IV1 to IV7. The inverter circuits IV1 to IV7 areconnected in series sequentially, and an output of the last stageinverter circuit IV7 is connected with an input of the first stageinverter circuit IV1. Outputs from the inverter circuits IV1 to IV7 areinput to the selection circuit 30 as polyphase reference clocks CK1 toCK7, respectively.

The digital VCO 20 outputs an output clock OCK including a frequencywhich fluctuates according to the value of a frequency control input Mfwhich is input from the frequency control terminal 40, and delay amountdata which indicates a phase difference between the phase of an idealclock calculated according to the value of the frequency control inputMf, and the phase of the abovementioned output clock OCK. This digitalVCO 20 operates with the reference clock CK1 as an operating clock.

The selection circuit 30 includes multiple D flip-flops FF1 to FF7 and aselector SELL The output clock OCK is input to each data input terminalD of the D flip-flops FF1 to FF7. Further, the reference clocks CK1 toCK7 are input to each clock input terminal of the D flip-flops FF1 toFF7. Then, each data output terminal Q outputs delay clocks F1 to F7 atrising edges of the reference clocks CK1 to CK7. The selector SEL1selects one of the delay clocks F1 to F7 according to the delay amountdata, and outputs the selected delay clock to the high precision clockoutput terminal 50.

Such PLL circuit 1 can output a high precision clock which includes highphase precision to the clock signal which should be output from the highprecision clock output terminal 50.

SUMMARY

In recent years, record and reproduction speed of data to and from anoptical disc media of an optical disc apparatus, such as CD and DVD, israpidly increasing. Thus, the abovementioned polyphase reference clockoutput circuit 10 of the PLL circuit 1 disclosed in Japanese UnexaminedPatent Application Publication No. 2008-205730 needs to increase thefrequency of the reference clock to generate. Moreover, as the referenceclock CK1 from the polyphase reference clock output circuit 10 is usedas the operating clock, the digital VCO 20 also needs to operate at highspeed. Such high frequency operation of the digital VCO 20 increases thepower consumption of the PLL circuit 1.

Further, there is an optical disc apparatus which can operate only withthe power supply from an interface such as USB in consideration ofadvantages, such as convenience, portability, and space-saving. However,there is a limitation in the power supplied from the interface such asUSB, thus the optical disc apparatus is required to reduce the powerconsumption. Accordingly, if the power is supplied from the power supplysuch as AC adapter to such optical disc apparatus, and there is noproblem in the power consumption (this case is hereinafter referred toas a high speed operation mode), data is recorded and reproduced to anoptical disc apparatus at high speed. On the other hand, in order tooperate only with the power supply from the interface such as USB andreduce the power consumption as much as possible (this mode ishereinafter referred to as a low power consumption mode), the record andreproduction speed of data to and from the optical disc apparatus isreduced so as to lower the power consumption.

However, the digital VCO 20 of the PLL circuit 1 only uses the referenceclock CK1 as an operating clock. Therefore, the present inventor hasfound a problem that if the capability of the high speed operation inthe high speed operation mode of an optical disc apparatus is increased,and the frequency of the reference clock generated by the polyphasereference clock output circuit 10 is increased, the power consumption ofthe digital VCO 20 will increase accordingly. In this case, even whentrying to reduce the power consumption as low as possible in the lowpower consumption mode of the optical disc apparatus, the powerconsumption of the digital VCO 20 increases as mentioned above, and itis not possible for the PLL circuit 1 to operate with low powerconsumption. Therefore, it is desired to realize a PLL circuit which canoperate the digital VCO with an optimal operating clock in the highspeed operation mode and the lower power consumption mode of the opticaldisc apparatus.

An exemplary aspect of the present invention is a PLL circuit thatincludes a polyphase reference clock output circuit that outputs aplurality of reference clocks with different phases, a polyphasefrequency divider circuit that outputs a plurality of divided clocks,where the plurality of divided clocks are obtained by dividingfrequencies of the plurality of reference clocks by a predeterminedvalue, a selection switch circuit that selects one of the plurality ofreference clocks or one of the plurality of divided clocks, and outputsthe selected clock as a selected clock, a digital VCO that uses theselected clock as an operating clock, and outputs delay amount dataindicating a phase difference between an output clock and an idealphase, where the output clock includes a frequency that fluctuatesaccording to a value of frequency control input data, and the idealphase is calculated according to the output clock and the value of thefrequency control input data, and a selection circuit that selects andoutputs the output clock, where the output clock is synchronized withone of the plurality of divided clocks according to the delay amountdata.

In the PLL circuit according to the present invention, a selectionswitch circuit selects either the reference clock output from thepolyphase reference clock output circuit or the divided clock outputfrom the polyphase frequency divider circuit. Then, the digital VCOoperates with the clock selected by the selection switch circuit as anoperating clock. The divided clock is obtained by dividing the frequencyof the reference clock by a predetermined value, thus the clockfrequency of the divided clock is lower than that of the referenceclock. Therefore, in order to operate the digital VCO at high speed, theselection switch circuit selects the reference clock, and in order toreduce the power consumption of the digital VCO, the selection switchcircuit selects the divided clock. Thus it is possible to operate thedigital VCO with an optimal operating clock.

The operation mode of the PLL circuit according to the present inventioncan be variable which enables both the high speed operation and the lowpower consumption operation as necessary.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other exemplary aspects, advantages and features will bemore apparent from the following description of certain exemplaryembodiments taken in conjunction with the accompanying drawings, inwhich:

FIG. 1 is a circuit block diagram of a PLL circuit according to a firstexemplary embodiment;

FIG. 2 is a circuit block diagram of a polyphase reference clock outputcircuit according to the first exemplary embodiment;

FIG. 3 is a circuit block diagram of a polyphase divide-by-two circuitaccording to the first exemplary embodiment;

FIG. 4 is a timing chart illustrating the operation of the polyphasedivide-by-two circuit according to the first exemplary embodiment;

FIG. 5 is a block diagram of a digital VCO according to the firstexemplary embodiment;

FIG. 6 is a timing chart explaining the operation of the digital VCOaccording to the first exemplary embodiment;

FIG. 7 is a timing chart illustrating the operation of the PLL circuitaccording to the first exemplary embodiment;

FIG. 8 is a circuit block diagram of a PLL circuit according to a secondexemplary embodiment;

FIG. 9 is a block diagram illustrating the connection configuration ofthe PLL circuit according to the second exemplary embodiment and afrequency divider circuit connected with the PLL circuit;

FIG. 10 is a circuit block diagram of a divide-by-1.5 circuit accordingto the second exemplary embodiment;

FIG. 11 is a logical value table explaining the relationship between aninput and an output of the divide-by-1.5 circuit and logical values ofinternal nodes according to the second exemplary embodiment;

FIG. 12 is a timing chart illustrating the operation of thedivide-by-1.5 circuit according to the second exemplary embodiment;

FIG. 13 is a block diagram of an optical disc apparatus according to thesecond exemplary embodiment;

FIG. 14 is a block diagram of an optical disc apparatus according to arelated art;

FIG. 15 is a table for comparing the clock frequency of each unit of theoptical disc apparatus according to the second exemplary embodiment andthe optical disc apparatus according to the related art;

FIG. 16 is a circuit block diagram of a PLL circuit according to otherexemplary embodiment; and

FIG. 17 is a circuit block diagram of a PLL circuit according to a priorart.

DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS First ExemplaryEmbodiment

Hereafter, a specific first exemplary embodiment incorporating thepresent invention is described with reference to the drawings. The firstexemplary embodiment applies the present invention to a PLL circuit ofan optical disc apparatus.

The configuration of a PLL circuit 100 according to the first exemplaryembodiment is illustrated in FIG. 1. As illustrated in FIG. 1, the PLLcircuit 100 includes a polyphase reference clock output circuit 110, adigital VCO 120, a selection circuit 130, a frequency control terminal140, a high precision clock output terminal 150, a polyphasedivide-by-two circuit 160, and a selector 170.

The polyphase reference clock output circuit 110 outputs referenceclocks CK1 to CK8, which are turned into multiphase clocks. Suppose thatthe reference clocks CK1 to CK8 shall have different phases from eachother. For example, the reference clocks CK1 to CK8 have clock waveformsshifted by 45 degrees in order.

An example of the configuration of the polyphase reference clock outputcircuit 110 is illustrated in FIG. 2. As illustrated in FIG. 2, thepolyphase reference clock output circuit 110 includes delay cellsDCEL111 to DCEL114 and buffer circuits BUF111 to BUF114.

The delay cells DCEL111 to DCEL114 input differential data from theprevious stage, respectively, and output the differential data to thesubsequent stages. Further, the delay cells DCEL111 to DCEL114 areconnected to form a ring as illustrated in FIG. 2. For example, aninverting output terminal and a non-inverting input terminal of thedelay cell DCEL111 are connected with a non-inverting input terminal andan inverting input terminal of the delay cell DCEL112, respectively.Similarly, an inverting output terminal and a non-inverting inputterminal of the delay cell DCEL112 are connected with a non-invertinginput terminal and an inverting input terminal of the delay cellDCEL113, respectively. An inverting output terminal and a non-invertinginput terminal of the delay cell DCEL113 are connected with anon-inverting input terminal and an inverting input terminal of thedelay cell DCEL114, respectively. An inverting output terminal and anon-inverting input terminal of the delay cell DCEL114 are connectedwith a non-inverting input terminal and an inverting input terminal ofthe delay cell DCEL111, respectively.

The buffer circuits BUF111 to BUF114 convert the level of an inputsignal into a signal level suited for the circuit connected in thesubsequent stage. The buffer circuits BUF111 to BUF114 also input thedifferential data from the previous stages, respectively, and output thedifferential data to the subsequent stages. For example, the buffercircuit BUF111 inputs the inverting output signal and the non-invertingoutput signal of the delay cell DCEL111 into a non-inverting inputterminal and an inverting input terminal, respectively. Then, thereference clocks CK1 and CK5 are output from the inverting outputterminal and the non-inverting output terminal, respectively.

Similarly, the buffer circuit BUF112 inputs the inverting output signaland the non-inverting output signal of the delay cell DCEL112 into anon-inverting input terminal and an inverting input terminal,respectively. Then, the reference clocks CK6 and CK2 are output from theinverting output terminal and the non-inverting output terminal,respectively. The buffer circuit BUF113 inputs the inverting outputsignal and the non-inverting output signal of the delay cell DCEL113into a non-inverting input terminal and an inverting input terminal,respectively. Then, reference clocks CK3 and CK7 are output from aninverting output terminal and a non-inverting output terminal,respectively. The buffer circuit BUF114 inputs the inverting outputsignal and the non-inverting output signal of the delay cell DCEL114into a non-inverting input terminal and an inverting input terminal,respectively. Then, reference clocks CK4 and CK8 are output from theinverted output terminal and the non-inverting output terminal,respectively.

The above configuration enables the polyphase reference clock outputcircuit 110 to output the reference clocks CK1 to CK8 having phase stepsof 45 degrees. Note that the number of stages of the abovementioneddelay cells may be further increased, the phase step may be smaller than45 degrees, and eight or more reference clocks may be output.

The polyphase divide-by-two circuit 160 divides the frequencies of thereference clocks CK1 to CK8, and outputs the divided clocks O1 to O16.However, the phase differences of the divided clocks O1 to O16 includethe clock waveforms having the phase step of 45 degrees in a similar wayas the reference clocks CK1 to CK8. FIG. 3 illustrates an example of theconfiguration of the polyphase divide-by-two circuit 160. As illustratedin FIG. 3, the polyphase divide-by-two circuit 160 includes D flip-flopsFF31 to FF38, FF41 to FF48, and an inverter circuit IV161.

The D flip-flop FF31 inputs the reference clock CK1 into a clock inputterminal, inputs an output signal from the inverter circuit IV161 into adata input terminal D, and outputs the divided clock O1 from the datainput terminal D. The D flip-flop FF32 inputs the reference clock CK8into a clock input terminal, inputs the divided clock O1 into a datainput terminal D, and outputs the divided clock O8 from the data inputterminal D. The D flip-flop FF33 inputs the reference clock CK7 into aclock input terminal, inputs the divided clock O8 into a data inputterminal D, and outputs the divided clock O15 from the data inputterminal D. The D flip-flop FF34 inputs the reference clock CK6 into aclock input terminal, inputs the divided clock O15 into a data inputterminal D, and outputs the divided clock O6 from the data inputterminal D.

The D flip-flop FF35 inputs the reference clock CK5 into a clock inputterminal, inputs the divided clock O6 into a data input terminal D, andoutputs the divided clock O13 from the data input terminal D. The Dflip-flop FF36 inputs the reference clock CK4 into a clock inputterminal, inputs the divided clock O13 into a data input terminal D, andoutputs the divided clock O4 from the data input terminal D. The Dflip-flop FF37 inputs the reference clock CK3 into a clock inputterminal, inputs the divided clock O4 into a data input terminal D, andoutputs the divided clock O11 from the data input terminal D. The Dflip-flop FF38 inputs the reference clock CK2 into a clock inputterminal, inputs the divided clock O11 into a data input terminal D, andoutputs the divided clock O2 from the data input terminal D.

The D flip-flop FF41 inputs the reference clock CK1 into a clock inputterminal, inputs the divided clock O2 into a data input terminal D, andoutputs the divided clock O9 from the data input terminal D. The Dflip-flop FF42 inputs the reference clock CK8 into a clock inputterminal, inputs the divided clock O9 into a data input terminal D, andoutputs the divided clock O16 from the data input terminal D. The Dflip-flop FF43 inputs the reference clock CK7 into a clock inputterminal, inputs the divided clock O16 into a data input terminal D, andoutputs the divided clock O7 from the data input terminal D. The Dflip-flop FF44 inputs the reference clock CK6 into a clock inputterminal, inputs the divided clock O7 into a data input terminal D, andoutputs the divided clock O14 from the data input terminal D.

The D flip-flop FF45 inputs the reference clock CK5 into a clock inputterminal, inputs the divided clock O14 into a data input terminal D, andoutputs the divided clock O5 from the data input terminal D. The Dflip-flop FF46 inputs the reference clock CK4 into a clock inputterminal, inputs the divided clock O5 into a data input terminal D, andoutputs the divided clock O12 from the data input terminal D. The Dflip-flop FF47 inputs the reference clock CK3 into a clock inputterminal, inputs the divided clock O12 into a data input terminal D, andoutputs the divided clock O3 from the data input terminal D. The Dflip-flop FF48 inputs the reference clock CK2 into a clock inputterminal, inputs the divided clock O3 into a data input terminal D, andoutputs the divided clock O10 from the data input terminal D.

The inverter circuit IV161 inputs the divided clock O1, and outputs aninverting signal thereof to the data input terminal of the D flip-flopFF31.

FIG. 4 is an operation timing chart of the polyphase divide-by-twocircuit 160 with the above configuration. As illustrated in FIG. 4, theD flip-flop FF31 latches the high level signal of the inverter circuitIV161, and outputs it as the divided clock O1 at the time t1 a, which isa rising edge timing of the reference clock CK1. Note that the Dflip-flop FF31 latches the low level signal of the inverter circuitIV161, and outputs it as the divided clock O1 at the time t1 b, which isa rising edge timing of the reference clock CK1. Therefore, the dividedclock O1 is a clock signal obtained by dividing the reference clock CK1by two.

The D flip-flop FF32 latches the divided clock O1, and outputs it as thedivided clock O1 at the timing t2, which is a rising edge timing of thereference clock CK8. The D flip-flop FF33 latches the divided clock O8,and outputs it as the divided clock O15 at the timing t3, which is arising edge timing of the reference clock CK7. Similarly, each of the Dflip-flops FF34 to FF38, and FF41 to FF48 latches and outputs theoutputs from the previous stage D flip-flops, respectively, at the timet4 to t16. Note that as a similar operation is carried out before thetime t1, the polyphase divide-by-two circuit 160 outputs the dividedclocks O1 to O16 having phase steps of 45 degrees, as a result.

The selector 170 (selection switch circuit) selects either the referenceclock CK1, which is output from the abovementioned polyphase referenceclock output circuit 110, or the divided clock O1, which is output fromthe polyphase divide-by-two circuit 160, and outputs the selected clockto the digital VCO 120. Note that the clock signal input to the selector170 is not limited to the reference clock CK1 and the divided clock O1.That is, the selector 170 may input one of the reference clocks CK1 toCK8, or one of the divided clocks O1 to O16.

The frequency control terminal 140 is an input terminal of frequencycontrol input data Mf which specifies the frequency of the output clockoutput from the digital VCO 120. Note that this frequency control inputdata Mf has a value corresponding to a rotation synchronizing signalobtained from wobble of an optical disc, such as CD.

The digital VCO 120 operates with the reference clock CK1 or the dividedclock O1 selected by the selector 170 as an operating clock. If thereference clock CK1 is used as the operating clock of the digital VCO120, the frequency of the reference clock CK1 is desirably specified tobe higher than the maximum frequency of the output clock OCK output fromthe digital VCO 120. The digital VCO 120 outputs the output clock OCKhaving the frequency which fluctuates according to the value of thefrequency control input data Mf. Further, the digital VCO 120 outputsthe delay amount data that indicates a phase difference between thephase of the output clock OCK and the phase of an ideal clock calculatedaccording to the value of the frequency control input data Mf. Note thatthe ideal clock is a target clock to synchronize a rising edge of a highprecision clock output from the PLL circuit 100. The phase of this idealclock is hereinafter referred to as an ideal phase.

FIG. 5 is a block diagram of the digital VCO 120. As illustrated in FIG.5, the digital VCO 120 includes an adder 121, a decoder 122, and aregister 123. As mentioned above, the digital VCO 120 operates with thereference clock CK1 or the divided clock O1 selected by the selector 170as the operating clock.

The adder 121 adds the frequency control input data Mf and internalphase information Np, whenever a rising edge of the operating clock isinput. The decoder 122 generates the output clock OCK, the delay amountdata, and a remainder calculation output Ro according to the calculationresult pf the adder 121 and the frequency control input data Mf. Theregister 123 stores the remainder calculation output Ro generated by thedecoder 122. The value of the remainder calculation output Ro stored inthe register 123 is the internal phase information Np at the nexttiming.

The decoder 122 includes a remainder calculator 124, a comparator 125, adelay data calculator 126, and a register 127. The remainder calculator124 divides the value (Mf+Np) input from the adder 121 by the value K(Mf<<K), which is the value calculated by adding 1 to the maximum valueof the internal phase information. Then, the remainder ((Mf+Np)modK) isoutput to the comparator 125 and the delay data calculator 126 as theremainder calculation output Ro. Note that (A mod B) indicates aremainder when dividing A by B. If the remainder calculation output Roinput from the remainder calculator 124 is smaller than K/2, thecomparator 125 outputs “1”. If the remainder calculation output Ro inputfrom the remainder calculator 124 is larger than K/2, the comparator 125outputs “0”. The delay data calculator 126 computes the delay amountdata according to the phase of the ideal clock, which is computed usingthe remainder calculation output Ro input from the remainder calculator124 and the frequency control input data Mf, and the phase of the outputclock OCK. The register 127 stores the computed delay amount data. Then,the register 127 outputs the delay amount data to the selection circuit130 at a predetermined timing.

The operation of the decoder 122 is explained hereinafter. The adder 121and the decoder 122 synchronize with the reference clock CK1 or thedivided clock O1 selected by the selector 170 to operate (the clockselected and output by the selector 170 is hereinafter referred to as areference operating clock). Therefore, each value output from the adder121 and the decoder 122 is updated at the clock cycle of the referenceoperating clock as unit time. Thus, if each unit of the digital VCO 120repeatedly carries out processes for each clock cycle of the referenceoperating clock, the internal phase information Np increases by Mf ateach clock frequency.

Suppose that the clock frequency of the reference operating clock isFref, the oscillating frequency Fock of the output clock OCK output fromthe comparator 125 is expressed as (Fref×Mf/K). If K/Mf is an integer N,the clock frequency F of the output clock OCK is to be a clock frequencywith a constant cycle obtained by dividing Fref by N. However, if K/Mfis not an integer (in other words, if K/Mf=N+α(0<α<1)), the output clockOCK is obtained as a mixed clock including the clock having N/Fref cycleand the clock having (N+1)/Fref cycle.

The delay data calculator 126 computes the difference of the phase ofthe ideal clock and that of the output clock OCK by processing theinternal phase information Np. To be more specific, the delay datacalculator 126 calculates (Mf−1−Np)/Mf, when a rising edge of the outputclock OCK is input, and outputs the calculation result to the register127.

FIG. 6 is a timing chart illustrating the operation of the decoder 122.The graph of FIG. 6 uses the value of the internal phase information Npfor the vertical axis, and time for the horizontal axis, to indicate thechange of the internal phase information Np. FIG. 6 also includes apattern diagram with the same time axis as the above graph, whichillustrates the phase difference of the output clock OCK and the idealclock.

As illustrated in FIG. 6, if Mf is a constant value, the value of NP isplotted in the shape of sawtooth wave. The timing when the value of Npexceeds the predetermined threshold (Mf−1) shall be defined as an idealphase. In this case, the difference between the value of Np and (Mf−1)at a rising edge timing of the output clock OCK is proportional to thedifference between the output timing of the output clock OCK and theideal phase. In other words, if Mf is a constant value, the time untilthe value of Np exceeds Mf−1 at the output timing of the output clockOCK can be computed by dividing (Mf−1−Np) by Mf.

The delay amount data can be defined by determining where in the orderof time zone the moment is included when the value of Np reaches Mf−1,if the clock cycle of the reference operating clock is equallytime-shared by any integer of 2 or more. For example, when the delaydata calculator 126 equally divides one cycle (1/Fref) of the referenceoperating clock by m (m is an integer of 2 or more) to compute the delayamount data, if T<t<=T+1−/m×Fref, where the output timing of the outputclock OCK is T and the timing of the ideal phase is t, then the value ofthe delay amount data is 1. If T+1−/m×Fref<t≦T+2−/m×Fref, the value ofthe delay amount data is 2. Accordingly, in general, it isT+n/m×Fref<t≦T+(n+1)/m×Fref (n is a natural number of m or less). Notethat if T=t, the phase difference between the output clock OCK and theideal clock is 0, thus the value of the delay amount data is 0. In thefirst exemplary embodiment, m=16.

The delay data calculator 126 outputs the delay amount data calculatedby the abovementioned calculation method to the register 127. Then, theregister 127 temporarily stores the delay amount data and outputs it tothe selection circuit 130.

The operation of the digital VCO 120 has been explained so far. Notethat the digital VCO 120 operates with the reference operating clock asthe operating clock, and the reference operating clock is either thereference clock CK1 or the divided clock O1 selected by the selector170. The divided clock O1 is obtained by dividing the frequency of thereference clock CK1 by two. Therefore, the operation speed of thedigital VCO 120 when using the divided clock O1 as the referenceoperating clock is approximately half of when using the reference clockCK1 as the reference operating clock. In other words, this means that ifthe dividing clock O1 is used as the reference operating clock, thepower consumption of the digital VCO 120 can be approximately half ofwhen using the reference clock CK1 as the reference operating clock. Onthe contrary, if the reference clock CK1 is used as the referenceoperating clock, the operation speed can be doubled as compared to whenusing the divided clock O1 as the reference operating clock. However, itis needless to say that the power consumption increases as compared towhen using the divided clock O1 as the reference operating clock.

The selection circuit 130 includes D flip-flops FF11 to FF26 and aselector SEL131. The D flip-flops FF11 to FF26 input the output clockOCK into their data input terminals D, respectively. Further, the Dflip-flops FF11 to FF26 input divided clocks O1 to O16 into their clockinput terminals, respectively. If the rising edges of the divided clocksO1 to O16 are input into each of the clock input terminals,respectively, the D flip-flops FF11 to FF26 hold the logical valuesinput into their data input terminals D, and output the logical valuesas delay clocks F1 to F16 from their data output terminals Q. Theselector SEL131 selects and outputs one of the delay clocks F1 to F16output from the D flip-flops FF11 to FF26 according to the value of thedelay amount data.

The high precision clock output terminal 150 outputs the delay clockoutput from the selector SEL131 to an external circuit as a highprecision clock HQCK, which is an output from the PLL circuit 100.

FIG. 7 is the timing chart illustrating the operation of the PLL circuit100 with the above configuration. Note that in the example of FIG. 7,signal delay in the selector SEL131 is not taken into consideration. Forthe sake of simplicity of the drawing, the reference clocks CK1 to CK8are omitted. The case in which the selector 170 selects the dividedclock O1 is considered hereinafter.

First, in the PLL circuit 100, the polyphase reference clock outputcircuit 110 outputs eight layers of the reference clocks CK1 to CK8. Thepolyphase divide-by-two circuit 160 outputs the divided clocks O1 toO16, which are obtained by dividing the reference clocks CK1 to CK8 bytwo. The selector 170 selects the divided clock O1, and outputs it tothe digital VCO 120 as the reference operating clock. Then, the digitalVCO 120 outputs the output clock OCK synchronized with the divided clockO1, and the delay amount data which changes its value by synchronizingwith a rising edge of the output clock OCK.

In the selection circuit 130, the D flip-flops FF11 to FF26 latch thelogical value of the output clock OCK in response to the divided clocksO1 to O16 which are input to the clock input terminals respectively, andoutput the logical value as the delay clocks F1 to F16. That is, therising edges of the delay clocks F1 to F16 are synchronized with thedivided clocks O1 to O16 to be output. The selector SEL131 selects oneof the delay clocks F1 to F16 according to the value of the delay amountdata from the digital VCO 120.

For example, if the delay amount data is 16, the selector SEL131 selectsand outputs the delay clock F16. This delay clock F16 is output as thehigh precision clock HQCK from the high precision clock output terminal150. The value of the delay amount data is computed from the differencebetween the ideal phase and the phase of the output clock OCK by thedigital VCO 120. If the delay amount data is 1, the selector SEL131selects and outputs the delay clock F1. The delay clock F1 is output asthe high precision clock HQCK from the high precision clock outputterminal 150. If the delay amount data is 8, the selector SEL131 selectsand outputs the delay clock F8. This delay clock F8 is output as thehigh precision clock HQCK from the high precision clock output terminal150.

The delay amount of the delay clocks F1 to F16 is generated according tothe delay amount of the divided clocks O1 to O16. Accordingly, the delayamount is adjusted to have a smaller step than the phase adjusting widthof the output clock OCK. Therefore, the clock output from the selectioncircuit 130 has a small phase difference from the ideal clock, and hasan extremely high phase precision. In the first exemplary embodiment,the clock output from the selection circuit 130 is referred to as thehigh precision clock.

In the abovementioned PLL circuit 100, the polyphase reference clockoutput circuit 110 outputs the reference clocks CK1 to CK8. Then, thepolyphase divide-by-two circuit 160 outputs the divided clocks O1 toO16, which are obtained by dividing the reference clocks CK1 to CK8 bytwo. These divided clocks O1 to O16 include the phase difference betweenthe reference clocks CK1 to CK8. Then, the D flip-flops FF11 to FF26latch the output clock OCK generated by the digital VCO at clock timingsof the divided clocks O1 to O16, and output them as polyphase delayclocks F1 to F16.

Then, the selector SEL131 outputs one of the delay clocks F1 to F16 asthe high precision clock HQCK according to the delay amount data outputfrom the digital VCO 120. Either the reference clock CK1 or the dividedclock O1 selected by the selector 170 is used as the operating clock ofthe digital VCO 120. If the selector 170 uses the divided clock O1,which has a lower frequency than the reference clock CK1, as theoperating clock, the power consumption of the digital VCO 120 can belowered. On the contrary, if the selector 170 selects the referenceclock CK1, the digital VCO 120 can operate at high speed. That is, it ispossible to select the operation of the digital VCO 120 either low speedbut low power consumption or high power consumption but high speedoperation relative to the operation mode of the PLL circuit 100.

For example, if the power is supplied from AC adaptor or the like to anoptical disc apparatus provided with the PLL circuit 100, and there isno problem in the power supply to the PLL circuit 100 or motor etc., thespeed of record and reproduction of data can be increased by speeding upthe rotation of an optical disc media, for example. In this case, thehigh speed operation of the digital VCO 120 can be possible if theselector 170 selects the reference clock CK1. Further, as the rotationalspeed of the optical disc media increases, the value of the frequencycontrol input data Mf increases accordingly. Thus, the increase speed ofthe internal phase information Np for each reference operating clock(1/Fref) also increases, so does the clock frequency of the output clockOCK. As described above, if the reference clock CK1 having high clockfrequency is used as the reference operating clock and the operationspeed of the digital VCO 120 is increased, the cycle of the referenceoperating clock can be shortened. This enables to generate the outputclock OCK accurately.

On the contrary, if the optical disc apparatus including the PLL circuit100 operates only with the power supply from an interface such as USB,the power supply is limited. Thus the optical disc apparatus enters thelow power consumption mode, and the power consumption of the PLL circuit100 must be reduced as well. In this case, if the selector 170 selectsthe divided clock O1, the power consumption of the digital VCO 120 canbe reduced, and thereby enabling to reduce the power consumption of thePLL circuit 100. In order to reduce the power consumption of a motor orthe like, the rotational speed of the optical disc media is reduced. Insuch case, the value of the frequency control input data Mf decreases.Therefore, the increase speed of the internal phase information Np foreach reference operating clock (1/Fref) slows down and the clockfrequency of the output clock OCK also decreases. As the divided clockO1 having low clock frequency is used as the reference operating clockas described above, the operation speed of the digital VCO 120 isreduced, however as the clock frequency of the output clock OCK is alsoreduced, there is no problem in the accuracy for generating the outputclock OCK.

As described so far, by switching the operating clock of the digital VCO120 according to the operation mode of an optical disc apparatusprovided with the PLL circuit 100, an optimal operation for the PLLcircuit 100 such as high speed operation and low power consumption canbe possible, therefore resolving the problem of the PLL circuit 1.

Second Exemplary Embodiment

A specific second exemplary embodiment incorporating the presentinvention is explained in detail with reference to the drawings. Thesecond exemplary embodiment applies the present invention to a PLLcircuit of an optical disc apparatus in a similar way as the firstexemplary embodiment.

FIG. 8 illustrates the configuration of a PLL circuit 200 according tothe first exemplary embodiment. As illustrated in FIG. 8, the PLLcircuit 200 includes a polyphase reference clock output circuit 110, a,digital VCO 120, a selection circuit 130, a frequency control terminal140, a high precision clock output terminal 150, a polyphasedivide-by-two circuit 160, a selector 170, a polyphase buffer circuit210, and external output terminals T1 to T8. Note that the symbols inFIG. 8 with the same symbols in FIG. 18 indicate the same or similarcomponents in FIG. 1. The difference from the first exemplary embodimentis that the PLL circuit 200 further includes the polyphase buffercircuit 210 and the external output terminals T1 to T8. Accordingly, theexplanation of the second exemplary embodiment focuses on thedifference, and omits the explanation of the same or similar componentsas FIG. 1.

The polyphase buffer circuit 210 inputs the reference clocks CK1 to CK8from the polyphase reference clock output circuit 110, performs currentbuffering, and outputs clocks B1 to B8, and C1 to C8 which have the samephase as the reference clocks CK1 to CK8. The clocks B1 to B8 are inputto the subsequent stage polyphase divide-by-two circuit 160. The clocksB1 to B8 are processed substantially in a similar manner as thereference clocks CK1 to CK8 in the first exemplary embodiment. After theclocks B1 to B8 are input to the polyphase divide-by-two circuit 160,similar processes as in the first exemplary embodiment are performed.

The polyphase buffer circuit 210 includes buffer circuits BUF21 toBUF28, respectively. The buffer circuits BUF21 to BUF28 include threeinverter circuits, respectively. Further, the buffer circuits BUF21 toBUF28 input the reference clocks CK1 to CK8, respectively, and outputthe clocks B1 to B8, and C1 to C8. For example, the buffer circuit BUF21includes inverter circuits IV21 to IV23. The inverter circuit IV21inputs the reference clock CK1, and outputs an output signal to inputterminals of the inverter circuits IV22 and IV23. The inverter circuitIV22 inputs an output signal from the inverter circuit IV21, and outputsan output signal as the clock B1. The inverter circuit IV23 inputs theoutput signal from the inverter circuit IV21, and outputs an outputsignal as the clock C1. The other buffer circuits BUF22 to BUF28 havethe same configuration as the buffer circuit BUF21.

The external output terminals T1 to T8 output the clocks C1 to C8.

As illustrated in FIG. 9, a part of the clocks C1 to C8 output from theexternal output terminals T1 to T8 are input to frequency dividercircuits 221 to 22 n (n is a natural number of 2 or more). Then, thefrequency divider circuits 221 to 22 n output divided clocks DIV1.5, andDIV2 to DIVn, which are obtained by dividing the clock frequencies ofthe clocks C1 to C8 by a predetermined value. For example, in theexample of FIG. 9, the frequency divider circuit 221 inputs the clocksC1 and C7, divides them by 1.5 and generates the clock DIV1.5.

Other frequency divider circuits 222 to 22 n input the clock C3, dividesby two to N, and generates clocks DIV2 to DIVn. Note that the clocksused by the frequency divider circuit 221 is not limited to C1 and C7,but may be any two clocks shifted by 270 degrees. The frequency dividercircuits 222 to 22 n can use any clock from the clocks C1 to C8.

Note that the clocks C1 to C8 are obtained by simply performing acurrent buffer to the reference clocks CK1 to CK8. Therefore, thefrequency divider circuits 221 to 22 n substantially divide the clockfrequencies of the reference clocks CK1 to CK8 by 1.5, and two to N togenerate divided clocks. Accordingly, if the current driving capacity ofthe buffer circuits BUF111 to BUF114 of the polyphase reference clockoutput circuit 110 has a level which can sufficiently drive thesubsequent circuit, the polyphase buffer circuit 210 can be eliminated.In this case, the reference clocks CK1 to CK8 are directly output to theexternal output terminals T1 to T8, respectively.

FIG. 10 is a circuit block diagram of the frequency divider circuit 221.As illustrated in FIG. 10, the frequency divider circuit 221 includescircuit units UNI1 and UNI7, and an RS latch circuit RS211. The circuitunit UNI1 includes a NOR circuit NOR211, D flip-flops FF211 and FF212,NAND circuits NAND211 to NAND213, an inverter circuit IV211, and an ORcircuit OR211.

The D flip-flop FF211 connects a data input terminal D with a node A11,and a data output terminal Q with a node B11. The D flip-flop FF212connects a data input terminal D with the node B11, and a data outputterminal Q with a node C11. The clock C1 is input to the clock inputterminals of the D flip-flops FF211 and FF212.

As for the NOR circuit NOR211, one input terminal is connected with thenode B11, another input terminal is connected with the node C11, and anoutput terminal is connected with the node A11. As for the invertercircuit IV211, the clock C1 is input to an input terminal, and an outputterminal is connected with one input terminal of the NAND circuitNAND212.

As for the NAND circuit NAND211, the clock C1 is input to one inputterminal, another input terminal is connected with a node D11, and anoutput terminal is connected with one input terminal of the NAND circuitNAND213. As for the NAND circuit NAND212, one input terminal isconnected with the node C11, another input terminal of the outputterminal of the inverter circuit IV211, and an output terminal isconnected with another input terminal of the NAND circuit NAND213. Asfor the NAND circuit NAND213, one input terminal is connected with theoutput terminal of the NAND circuit NAND211, another input terminal isconnected with the output terminal of the NAND circuit NAND212, and anoutput terminal is connected with the node D11. As for the OR circuitOR211, one input terminal is connected with the node D11, another inputterminal is connected with the node B11, and an output terminal isconnected with the node E11. Hereinafter, a signal output from the ORcircuit 221 to the node E11 is referred to as a clock E11.

FIG. 11 is a table indicating logical values of each node A11, B11, C11,D11, and E11 for logical values of the clock C1, which is an inputsignal to the abovementioned circuit unit UN1. As illustrated in FIG.11, the clock duty ratio of the clock C1 is 1:1, whereas that of theclock E11 output to the node E11 is 2:1.

The circuit unit UNI7 includes a NOR circuit NOR271, D flip-flops FF271and FF272, NAND circuits NAND271 to NAND273, an inverter circuit IV271,and an OR circuit OR271.

As for the D flip-flop FF271, a data input terminal D is connected witha node A17, and a data output terminal Q is connected with a node B17.As for the D flip-flop FF272, a data input terminal D is connected withthe node B17, and a data output terminal Q is connected with a node C17.The clock C7 is input to clock input terminals of the D flip-flops FF271and FF272.

As for the NOR circuit NOR271, one input terminal is connected with thenode B17, another input terminal is connected with the node C17, and anoutput terminal is connected with the node A17. As for the invertercircuit IV271, the clock C7 is input to an input terminal, and an outputterminal is connected with one input terminal of the NAND circuitNAND272.

As for the NAND circuit NAND271, the clock C7 is input to one inputterminal, another input terminal is connected with a node D17, and anoutput terminal is connected with another input terminal of the NANDcircuit NAND273. As for the NAND circuit NAND272, one input terminal isconnected with the node C17, another input terminal is connected withthe output terminal of the inverter circuit IV271, and an outputterminal is connected with another input terminal of the NAND circuitNAND273. As for the NAND circuit NAND213, another input terminal isconnected with the output terminal of the NAND circuit NAND271, anotherinput terminal is connected with the output terminal of the NAND circuitNAND272, and an output terminal is connected with the node D17.

As for the OR circuit OR271, one input terminal is connected with thenode D17, another input terminal is connected with the node B17, and anoutput terminal is connected with a node E17. Hereinafter, a signaloutput from the OR circuit 271 to the node E17 is referred to as a clockE17.

The logical values of each node A17, B17, C17, D17, and E17 for thelogical value of the clock C7, which is an input signal to theabovementioned circuit unit UNI7, are substantially same as the logicalvalues of each node A11, B11, C11, D11, and E11 illustrated in FIG. 11.Therefore, the clock duty ratio of the clock C7 is 1:1, whereas that ofthe clock E17 output to the node E17 is 2:1. However, the phases of theclocks C1 and C7 are shifted by 270 degrees, thus it should be notedthat the phases of the clocks E11 and E17 are also shifted by 270degrees.

As for the RS latch circuit RS211, a reset terminal R is connected withthe node E11, and a set terminal S is connected with the node E17. Then,the divided-by-1.5 clock DIV1.5, which is the output of the frequencydivider circuit 221, is output from a data output terminal Q.

FIG. 12 is a timing chart indicating the operation of the frequencydivider circuit 221 having above configuration. The RS latch circuitRS211 performs similar operations as a usual RS latch circuit. That is,if a high level pulse signal is input to the set terminal S (node E11),and an output logical value is set to high level, whereas if a highlevel pulse signal is input to the reset terminal R (node F17), theoutput logical value is set to low level. Therefore, at the time t1, theclock E11 rises to high level, thus the 1.5 divided clock DIV1.5 alsorises to high level. At the time t1, the clock E17 rises to high level,thus the divided-by-1.5 clock DIV1.5 falls to low level. Similarly, atthe time t3, the clock E11 rises to high level, thus divided-by-1.5clock DIV1.5 also rises to high level. At the time t4, the clock E17rises to high level, thus the divide-by-1.5 clock DIV1.5 falls to lowlevel. Accordingly, the clock frequency of the divide-by-1.5 DIV1.5 isthe clock frequency of the clock C1 or C7 divided by 1.5.

The frequency divider circuit 221 has been explained so far. Otherfrequency divider circuits 222 to 22 n may be realized by theconfiguration of an existing general frequency divider circuit.Accordingly, the explanation of the configuration and the operationthereof is omitted, as it is well known in the art.

FIG. 13 is a block diagram of an optical disc apparatus 300 using suchPLL circuit 200, the frequency divider circuits 221 and 222. Asillustrated in FIG. 13, the optical disc apparatus 300 includes acontroller circuit 310 and an optical disc drive circuit 320. Thecontroller circuit 310 includes the abovementioned PLL circuit 200, thefrequency divider circuits 221 and 222, and a logic circuit 311. Theoptical disc drive circuit 320 includes a record data write and readcircuit 321. The record data write and read circuit 321 transmits thedata read from an optical disc, and a rotation synchronizing signalbased on the wobble of the optical disc to the controller circuit 310.The record data write and read circuit 321 inputs a recording clockgenerated according to the high precision clock HQCK, and the write datato record in accordance with this recording clock or the like, from thecontroller circuit 310, and records the data to the optical disc. Therecord data write and read circuit 321 further inputs a pickup requiredat the time of the recording process and control data for controllingthe motor from the controller circuit 310.

The logic circuit 311 uses 133 MHz and 100 MHz as a system clock. Inthis case, if the clock frequency of the reference clocks CK1 to CK8output from the polyphase reference clock output circuit 110 is 200 MHz,the frequency divider circuit 221 can generate a system clock 1 with 133MHz, which is divided by 1.5, and the frequency divider circuit 222 cangenerate a system clock 2 with 100 MHz, which is divided by two. Thenthe logic circuit 311 can operate with the system clocks 1 and 2 asoperating clocks.

That is, in the optical disc apparatus 300 of the second exemplaryembodiment, the system clock of the logic circuit 311 in the opticaldisc apparatus 300 is generated using the reference clock output fromthe polyphase reference clock output circuit 110 for generating the highprecision clock HQCK.

FIG. 14 illustrates an optical disc apparatus 400 according to a relatedart, which assumes the polyphase reference clock generated as in the PLLcircuit 1 in the first exemplary embodiment or Japanese UnexaminedPatent Application Publication No. 2008-205730 is not used externally.In this case, as illustrated in FIG. 14, a reference clock generatingcircuit 413 for usually generating the system clock of the logic circuit311 is prepared separately from the PLL circuit 1 for generating thehigh precision clock HQCK. Accordingly, the optical disc apparatus 400of FIG. 14 further requires the reference clock generation circuit 413for generating the system clocks as compared to the optical discapparatus 300 according to the second exemplary embodiment in FIG. 13.This means that the optical disc 400 has a larger circuit size than theoptical disc apparatus 300 for the reference clock generation circuit413. However, in the optical disc apparatus 300 of the second exemplaryembodiment, the reference clock output from the polyphase referenceclock output circuit 110 can be used to generate a system clock and asan operating clock of the PLL circuit 200. Therefore, it is possible toeliminate the circuit corresponding to the reference clock generatingcircuit 413, thereby enabling to reduce the circuit size. Moreover, thepower consumption can be reduced as the power to the reference clockgenerating circuit 413 is unnecessary.

Further, in the optical disc apparatus 400 according to the related art,if the reference clock generation circuit cannot generate referenceclocks with 270 degrees phase shift, and attempts to generate a systemclock 1 with 133 MHz, which is fractionally divided, the reference clockto output must be increased to 400 MHz. The reason for this is that asthe reference clock output circuit can only output a reference clockhaving a single frequency, a divide-by-three circuit 411 is requiredwhen trying to generate a system clock 1 with 133 MHz, which isfractionally divided. Note that a divide-by-four circuit 412 is used togenerate a system clock 2 with 100 MHz.

On the other hand, in the optical disc apparatus 300 of the secondexemplary embodiment, the polyphase reference clock output circuit 110outputs multiple reference clocks having 270 degrees phase shift (forexample, the reference clocks CK1 and CK7). Thus, by providing thefrequency divider circuit 221 of divide-by-1.5 as illustrated in FIG.10, the frequency of the reference clock output from the polyphasereference clock output circuit 110 can be suppressed to 200 MHz. As wellknown in the art, the power consumption of the circuit increases inproportion to the square of the operating frequency. Thus the powerconsumption of the reference clock output circuit 413 having 400 Mhzused in the optical disc apparatus 400 increases largely as compared tothe power consumption of the polyphase reference clock output circuit110 having 200 MHz, which is used in the optical disc apparatus 300according to the second exemplary embodiment. In other words, theoptical disc apparatus 300 of the second exemplary embodiment canoperate with lower power consumption as compared with the optical discapparatus 400.

FIG. 15 is a table that summarizes the above explanation for comparingeach clock frequency used in the optical disc apparatus 300 with eachclock frequency used in the optical disc apparatus 400 according to thesecond exemplary embodiment.

The present invention is not limited to the above exemplary embodiments,but can be modified as appropriate within the scope and the sprit of thepresent invention. For example, although the polyphase divide-by-twocircuit 160 that divides the reference clocks by two is used in thefirst exemplary embodiment, a polyphase divide-by-N circuit (N is aninteger of 2 or more) which divides the reference clocks CK1 to CK8 by Ncan be used instead. In the second exemplary embodiment, although thedivide-by-1.5 circuit 221 is used, a fractional frequency dividercircuit such as a divide-by-2.5 circuit, and divide-by-3.5 circuit maybe used. Moreover, if the phase step of the reference clock output fromthe polyphase reference clock output circuit 110 can be smaller than 45degrees, a frequency divider circuit, which outputs divided frequencies(for example, divide-by-1.1 and divide-by-1.2 frequencies etc.) of anyvalue that can be generated using the polyphase reference clock, may beused.

Further, as with the PLL circuit 500 illustrated in FIG. 16, the clockoutput to the external output terminals T1 to T8 may be the clocks C1 toC8 (hereinafter referred to a polyphase clock signal S1) from thepolyphase buffer circuit 210 selected by the selector SEL501 or thedivided clocks O1, O3, O5, O7, O9, O11, O13, or O15 (hereinafterreferred to as a polyphase clock signal S2) from the polyphasedivide-by-two circuit 160. Note that the symbols in FIG. 16 with thesame symbols in FIG. 8 indicate the same or similar components in FIG.8.

An exemplary advantage of replacing the PLL circuit 200 in the opticaldisc apparatus 300 of FIG. 13 with a PLL circuit 500 is explainedhereinafter. Further, suppose that the polyphase reference clock outputcircuit 110 outputs a reference clock having clock frequency of 200 MHz.

In this case, if a selector SEL501 selects a polyphase clock signal S1,the frequency divider circuit 221 generates a system clock 1 havingclock frequency of 133 MHz. Moreover, the frequency divider circuit 222generates a system clock 2 having clock frequency of 100 MHz. On theother hand, if the selector SEL501 selects a polyphase clock signal S2,the frequency divider circuit 221 generates a system clock 2 havingclock frequency of 66.6 MHz. Moreover, the frequency divider circuit 222generates a system clock 2 having clock frequency of 50 MHz. In thisway, by switching the signal selected by the selector SEL501, it ispossible to switch the frequency of the system clock to be supplied tothe logic circuit 311. Then, by reducing the system clock of thecontroller circuit 310 when the optical disc apparatus is set to the lowpower consumption mode, the power consumption of the optical discapparatus 300 can further be reduced.

The first and second exemplary embodiments can be combined as desirableby one of ordinary skill in the art.

While the invention has been described in terms of several exemplaryembodiments, those skilled in the art will recognize that the inventioncan be practiced with various modifications within the spirit and scopeof the appended claims and the invention is not limited to the examplesdescribed above.

Further, the scope of the claims is not limited by the exemplaryembodiments described above.

Furthermore, it is noted that, Applicant's intent is to encompassequivalents of all claim elements, even if amended later duringprosecution.

1. A PLL circuit comprising: a polyphase reference clock output circuitthat outputs a plurality of reference clocks with different phases; apolyphase frequency divider circuit that outputs a plurality of dividedclocks, the plurality of divided clocks being obtained by dividingfrequencies of the plurality of reference clocks by a predeterminedvalue; a selection switch circuit that selects one of the plurality ofreference clocks or one of the plurality of divided clocks, and outputsthe selected clock as a selected clock; a digital VCO that uses theselected clock as an operating clock, and outputs delay amount dataindicating a phase difference between an output clock and an idealphase, the output clock including a frequency that fluctuates accordingto a value of frequency control input data, and the ideal phase beingcalculated according to the output clock and the value of the frequencycontrol input data; and a selection circuit that selects and outputs theoutput clock, the output clock being synchronized with one of theplurality of divided clocks according to the delay amount data.
 2. ThePLL circuit according to claim 1, wherein the polyphase divider circuitsets a phase difference between divided clocks of the plurality ofdivided clocks to be same as a phase difference between reference clocksof the plurality of reference clocks.
 3. The PLL circuit according toclaim 1, wherein the digital VCO increases a frequency of the outputclock as the value of the frequency control data increases.
 4. The PLLcircuit according to claim 1, further comprising a first frequencydivider circuit that is connected with the PLL circuit, and outputs afirst clock, the first clock being obtained by dividing a clockfrequency of the plurality of reference clocks or the plurality ofdivided clocks by a predetermined value.
 5. The PLL circuit according toclaim 4, wherein the first frequency divider circuit outputs a firstclock, the first clock being obtained by fractionally dividing thefrequency of the plurality of reference clocks or the plurality ofdivided clocks.
 6. The PLL circuit according to claim 5, wherein thefirst frequency divider circuit outputs the first clock divided by 1.5using clocks with a 270 phase shift among the plurality of referenceclocks or the plurality of divided clocks.
 7. The PLL circuit accordingto claim 4, wherein the PLL circuit is used in an optical discapparatus, and the optical disc apparatus comprises: the PLL circuit;the first frequency divider circuit; and a logic circuit, wherein thelogic circuit operates using the first clock output from the firstfrequency divider circuit as a system clock.
 8. An optical discapparatus comprising: the PLL circuit according to claim 4; the firstfrequency divider circuit according to claim 4; and a logic circuit,wherein the logic circuit operates using the first clock output from thefirst frequency divider circuit as a system clock.